1. Field of the Invention
The present invention relates generally to a display device, and more particularly to a display device which is composed of a plurality of self-luminous elements.
2. Description of the Related Art
In recent years, organic electroluminescence (EL) display devices have attracted attention as flat-panel display devices. Since the organic EL display device is a self-luminous device, it has such features as a wide viewing angle, small thickness without a need for backlight, low power consumption, and a high responsivity speed.
For these features, the organic EL display device is a promising candidate for the next-generation plat-panel display device, which will take the place of liquid crystal display devices. The organic EL display device is configured such that a plurality of organic EL elements are arranged in a matrix. Each organic EL device has such a structure that an optical active layer containing an organic compound with a light-emitting function is sandwiched between an anode and a cathode.
There has been proposed a display device of this kind, which includes a first reflection film and a second reflection film that are so arranged as to sandwich an organic EL element which generates light with a peak wavelength λ. The optical path length of the organic EL element that is sandwiched between the first reflection film and the second reflection film is set at λ·m/2 (m is an integer of 1 or more).
According to this structure, it is possible to suppress attenuation of light of a selective wavelength due to interference occurring between the first reflection film and the second reflection film (see, e.g. Jpn. Pat. Appln. KOKAI Publication No. 2003-151761).
In a typical method for realizing an organic EL display device that is capable of color display, color pixels that emit red (R), green (G) and blue (B) light are arranged. However, since the wavelengths of red (R), green (G) and blue (B) are different, different optical path lengths need to be set in the respective color pixels in order to optimize the condition of interference. In short, different film thicknesses need to be set in the respective color pixels.
However, most of thin films, which constitute the respective color pixels, are commonly used, and it is very difficult to obtain optimal optical path lengths in the respective color pixels by adjusting the film thickness of each thin film. Moreover, since the conditions for optimizing the optical path length are different between the respective color pixels of red (R), green (G) and blue (B), it is difficult to meet conditions for, e.g. both the light extraction efficiency of a given color and the color purity of another color. Thus, there is such a problem that it is difficult to achieve both the increase in luminance and the increase in color purity.